Actually the ZL-1 and 1LE offsets are as follows:
20x10 fronts offset +23mm ( this will clear OEM struts with a 285/35/20 tire ) If you have some coil overs you can move the wheel/tire assembly inboard a bit with more positive offset such as +30mm
20x11 rears offset +43mm
GM picked these sizes and offsets so that the front and rear track would be the same on the ZL-1 and 1LE.
If you put a front 20x10 with +23mm offset ZL-1/1LE wheel on the rear the wheel will stick out .3" more than the 20x11 +43mm offset wheel on the rear. Pretty aggressive.
Ed M.